A prior art article entitled "The Friedel-Crafts Type Methanesulfonylation of Deactivated Benzenes" by Ono et al, Chemistry Letters, Vol. 3, pp. 395-398 (1988), teaches that the addition of a catalytic amount of trifluoromethanesulfonic acid in an excess of methane sulfonic anhydride is effective for methanesulfonylation of m-dichlorobenzene. The procedure is also taught to be useful for other deactivated benzenes such as p-nitrotoluene in a yield of about 55 percent. A typical procedure involved heating a solution of methanesulfonic acid and thionyl chloride under reflux for one hour to generate the methanesulfonic anhydride, cooling the reaction mixture to 25.degree. C., then adding p-nitrotoluene and trifluoromethane sulfonic acid. The whole mixture is heated to 120.degree. C. for three hours and cooled to 50.degree. C. for recovery of the sulfonylated product by conventional techniques.
Certain 2-(2'4'-disubstituted benzoyl)-1,3-cyclohexanedione herbicides are described in U.S. Pat. No. 4,780,127, issued Oct. 25, 1988, and incorporated herein by reference.
The above-described herbicidal compounds can have the following structural formula ##STR1## wherein R.sup.2 is C.sub.1 -C.sub.4 alkyl and R.sup.7 through R.sup.12 are hydrogen or C.sub.1 -C.sub.4 alkyl.
These herbicides can be prepared by reacting a dione of the structural formula ##STR2## wherein R.sup.7 through R.sup.12 are as defined with a gram molecular weight (mole) of disubstituted benzoyl chloride of the structural formula ##STR3## wherein R.sup.2 is as defined above. The acid chlorides are readily prepared from the corresponding carboxylic acids by those skilled in the art. In turn, the carboxylic acids may be prepared by oxidation of analogous alkylbenzene according to the formula ##STR4## where R is methyl or ethyl and R.sup.2 is a C.sub.1 -C.sub.4 alkyl residue. Both steps are taught in U.S. Pat. No. 4,780,127.